Status: No accepted records.
Taxonomy: No subspecies are recognized.
See related taxonomic discussions under Mallard and Mottled Duck.
Whether Mexican Duck is a valid species has been a matter of debate, although it was recently elevated to species status by AOS (Chesser et al 2020) based primarily on genomic studies by Lavretsky et al (2019). It had been considered by some authors, including AOU (1998), a subspecies (as A. p. diazi) of Mallard, A. platyrhynchos (see also Johnsgard 1975, Sibley and Monroe 1990). AOU denied a proposal by Banks to elevate it to species status citing a study by Hubbard (1977) who concluded there was “extensive introgression” with Mallard in the northern parts of Mexican Duck’s range; the AOU discussion can be found HERE. However, the evidence provided in Hubbard in support of this conclusion is at best equivocal: on a scale of 0-36 (“pure” Mexican Duck = 36) the scores ranged from 34.5 at the southern edge of its range to 28.3 in the north. While this shallow cline suggests Mallard introgression at some time in the past (McCracken et al 2001, Avise 1990) and to an uncertain extent currently (Lavretsky et al 2015, Leukering and Mlodinow 2012), recent studies have found assortative mating in areas where Mallard occurs with Mexican Duck (Bevill 1970, Webster 2006, Baldassarre 2014). Genetic studies by Lavretsky et al (2015, 2019) suggest that Mexican Duck and Mallard are in the early stages of divergence; mtDNA and Z-chromosome data show significant differentiation, “perhaps at a level that would warrant species recognition”. Very few Mallards occur in the breeding range of Mexican Duck during periods when pairing occurs (Baldassarre 2014, Leukering and Mlodinow 2012). For these reasons, we follow the decision of AOS (Chesser et al 2020) to elevate Mexican Duck to full species status. While there is evidence that American Black, Mottled, and Mexican Ducks all possess some degree of Mallard introgression, taxonomic consistency would also indicate treatment of Mexican Duck as a full species (Leukering and Mlodinow 2012, Drilling et al 2020). Studies are currently underway by Andrew Engilis attempting to provide a baseline for more accurate correlation of phenotype and genotype (Steven Mlodinow, pers. comm.).
For records of hybrids between Mexican Duck and Mallard, see Edit Post ‹ Birds of Nebraska – Online — WordPress (outdoornebraska.gov).
Comments: There are three reports. It is likely that more will occur northward as part of an ongoing low-density northward push into the Great Plains possibly due to severe drought in the southwestern US but also concomitant with northward range expansion in other southern waterbirds like Neotropic Cormorant and Black-bellied Whistling-Duck (Steven Mlodinow, pers. comm.).
The most recent report is of one with Mallards in a small pond near Grant, Perkins Co 14 Sep 2019 (https://ebird.org/checklist/S59808685). The description provided follows: “Overall, it had a dark brown body contrasting somewhat sharply with paler head and neck. The underparts were uniformly dark from chest thru undertail coverts. The tail was entirely brown. The speculum looked to have narrower borders than that of a MALL, more so to the rear than in front. The head and neck were pale brown with blackish on crown and with a blackish eyeline. No black mark at gape. No pale tan unstreaked area as in MODU. The bill was orange with dusky along culmen and towards tip. No distinct black blotches.” The report was not accepted by NOURC which stated: “Probably correct, but not beyond reasonable doubt” (Brogie 2020).
There are two older reports, neither accepted (Bray et al 1986, Silcock et al 1986). A specimen referred to as Mexican Duck was collected 17 Oct 1921 in Cherry Co (Bent 1923). This is a female #973 in the Field Museum of Natural History, Chicago, but is now considered likely a hybrid between Mallard and American Black Duck (David Willard, personal communication). The second report is of an adult male shot in Rock Co 19 Oct 1969 (Menzel 1970). Although its identity as a Mexican Duck was confirmed by Paul Johnsgard and the bird showed no evidence of captivity, the possibility of its being an escaped bird could not be eliminated (Menzel 1970). Menzel (1970) noted that at that time Mexican Ducks were kept in captivity in Hall Co and that escapes occurred occasionally.
A dark female mallard type paired with a male Mallard 20 Jun 1993 in Sioux Co and reported by Ross Silcock as an American Black Duck may have been a Mexican Duck or a Mallard x Mexican Duck hybrid based on current knowledge. The identification as American Black Duck was considered “Most unusual for season and location” (Grzybowski 1993).
There are numerous records for Colorado, east to Yuma and Kiowa Cos, adjacent to Nebraska (CBRC 2017, eBird.org accessed April 2021) but none for Kansas or Oklahoma (Thompson et al 2011, eBird.org accessed April 2021).
American Ornithologists’ Union [AOU]. 1983. The AOU Check-list of North American birds, 6th ed. Allen Press, Lawrence, Kansas, USA.
Baldassarre, G. 2014. Ducks, geese, and swans of North America. Johns Hopkins University Press, Baltimore, Maryland, USA.
Bellrose, F.C. 1976. Ducks, Geese & Swans of North America. Stackpole Books, Harrisburg, Pennsylviania, USA.
Bent, A.C. 1923. Life histories of North American wild fowl. Bulletin of the United States National Museum 126. Dover Publications Reprint 1962, New York, New York, USA.
Bevill, W.V., Jr. 1970. Effects of supplemental stocking and habitat development on abundance of Mexican Ducks. Master’s thesis, New Mexico State University, Las Cruces, New Mexico, USA.
Bray, T.E., B.K. Padelford, and W.R. Silcock. 1986. The birds of Nebraska: A critically evaluated list. Published by the authors, Bellevue, Nebraska, USA.
Brogie, M.A. 2020. 2019 (31st) Report of the NOU Records Committee. NBR 88: 124-134.
Chesser, R.T., S.M. Billerman, K.J. Burns, C. Cicero, J.L. Dunn, A.W. Kratter, I.J. Lovette, N.A. Mason, P.C. Rasmussen, J.V. Remsen Jr., D.F.and K. W Sixty-first Supplement to the American Ornithological Society’s Check-list of North American Birds. Auk 137, Issue 3, 1 July 2020, ukaa030, https://doi.org/10.1093/auk/ukaa030.
Colorado Bird Records Committee [CBRC]. 2017. Mottled Duck records. Colorado Bird Records Committee database, accessed November 2017.
Drilling, N., S.O. Williams III, R.D. Titman, and F. McKinney (2020). Mexican Duck (Anas diazi), version 1.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.mexduc.01.
Gill, F., D. Donsker, and P. Rasmussen (Eds). 2020. IOC World Bird List (v 10.2). Doi 10.14344/IOC.ML.10.2. http://www.worldbirdnames.org/.
Hubbard, J.H. 1977. The biological and taxonomic status of the Mexican Duck. Bull. New Mexico Dept. Game Fish 16.
Johnsgard, P.A. 1975. Waterfowl of North America. University of Indiana Press, Bloomington, Indiana, USA.
Lavretsky, P., J.M. DaCosta, B.E. Hernandez-Banos, A. Engilis Jr., M.D. Sorenson, and J.L. Peters. 2015. Speciation genomics and a role for the Z chromosome in the early stages of divergence between Mexican ducks and mallards. Molecular Ecology 24: 5364–5378.
Lavretsky, P., T. Janzen, and K.G. McCracken. 2019. Identifying hybrids & the genomics of hybridization: Mallards & American black ducks of Eastern North America. Ecology and Evolution 9: 3470-3490. https://doi.org/10.1002/ece3.4981Citations: 10.
Leukering, T., and S.G. Mlodinow. 2012. The Mexican Duck in Colorado: Identification and Occurrence. Colorado Birds 46: 296-309.
McCracken, K.G., W.P. Johnson, and F.H. Sheldon. 2001. Molecular population genetics, phylogeography, and conservation biology of the mottled duck (Anas fulvigula). Conservation Genetics 2: 87-102.
Menzel, K.E. 1970. Mexican Duck. NBR 38: 89-90.
Sibley, C.G., and B.L. Monroe, Jr. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, Connecticut, USA.
Silcock, W.R., T.E. Bray, and B.K. Padelford. 1986. Mexican Duck in Nebraska. NBR 54: 40-41.
Thompson, M.C., C.A. Ely, B. Gress, C. Otte, S.T. Patti, D. Seibel, and E.A. Young. 2011. Birds of Kansas. University Press of Kansas, Lawrence, Kansas, USA.
Webster. R. 2006. The Status of Mottled Duck (Anas fulvigula) in Arizona. Arizona Birds Online 2: 6-9.
Silcock, W.R., and J.G. Jorgensen. 2022. Mexican Duck (Anas diazi). In Birds of Nebraska — Online. www.BirdsofNebraska.org
Birds of Nebraska – Online
Updated 11 Mar 2022